A thermosetting resin which mainly contains a terminal-modified imide oligomer having a low molecular weight is highly heat-resistant. Accordingly, the thermosetting resin has been proposed and gradually used as a molding material or a matrix resin for a complex fibrous material.
For example, some addition polyimide resins having a terminal unsaturated group (imide oligomers) are proposed as a prepreg resin in Japanese Patent Provisional Publications No. 59(1984)- 167569, No. 60(1985)-250030, No. 60(1985)-260624, No. 60(1985)-260625 and No. 61(1986)-247733. The imide oligomers can be prepared, for example, by a reaction of an aromatic tetracarboxylic dianhydride such as pyromellitic dianhydride or benzophenonetetracarboxylic dianhydride, an aromatic diamine and an unsaturated reactive compound.
However, the above-mentioned conventional imide oligomer resins have some problems in preparation of themselves or the products using them. For example, some diamine compounds used in preparation of the oligomers are extremely specific and expensive. The imide oligomers are low in solubility in an organic solvent, so that it is difficult for the oligomers to permeate reinforcing fibers. Further, a high boiling organic solvent which is very specific should be used in preparation of a solution of the imide oligomers. Furthermore, the imide oligomer resins have such a high melting point that the products using them tend to deteriorate at elevated temperatures.
The known imide oligomers also have some problems in the curing property. In more detail, the time required for gelation of the oligomers is relatively long, and a terminal group having a cross linking function tends to remain reactive. Therefore, if a composite is made from the known oligomers, the mechanical strength and elasticity of the heat-cured product of the oligomers are insufficient. Further, the matrix made of the known imide oligomers does not have a sufficient affinity with reinforcing fibers, so that a debonding is sometimes caused.
To solve the above-mentioned problems, improved terminal-modified imide oligomers have been proposed in Japanese Patent Applications No. 62(1987)-29766, No. 63(1988)-73194 and No. 63(1988) 21373.
Though the newly proposed terminal-modified imide oligomers solve the above-mentioned problems, a further improvement with respect to heat-resistance, mechanical strength and elasticity of the heat-cured product made from the oligomers is needed to practically use the imide oligomers.
As is mentioned above, a satisfactory imide oligomer resin, which is improved in various natures such as processability, heat-resistance and mechanical property, has not yet been proposed in this technical field. Therefore, such a satisfactory imide oligomer resin has been desired.